Sialia mexicana

Western Bluebird

Family: Turdidae · Class: Aves · Order: Passeriformes

The Western Bluebird is a medium-sized thrush measuring 15-18 cm (6-7 inches) in length with a wingspan of 25-32 cm (10-13 inches). Males display brilliant azure blue upperparts, head, and wings, with rusty orange extending across the breast and sometimes onto the back between the shoulders. The belly and undertail coverts are gray to white. Females are predominantly gray-brown with blue-tinged wings and tail, and may show pale orange wash on the breast. Both sexes have dark legs and bills, with juveniles resembling females but showing spotted breasts typical of young thrushes. Western Bluebirds range from British Columbia south through western North America to central Mexico. In California, they occur throughout most of the state except for high desert regions and the Central Valley floor. The species is found from sea level to elevations of approximately 2,100 meters (7,000 feet), with breeding populations distributed across the Coast Ranges, Sierra Nevada foothills, and mountainous regions of southern California. Northern populations are partially migratory, moving to lower elevations or southern latitudes during winter. This species inhabits open woodlands, particularly oak savannas, riparian corridors, and forest edges. Western Bluebirds favor areas with scattered trees for nesting and perching, combined with open ground for foraging. They utilize natural tree cavities, old woodpecker holes, and nest boxes placed 1.5-6 meters (5-20 feet) above ground. Suitable habitat includes oak woodlands, pine-oak forests, logged areas with snags, orchards, and rural residential areas with appropriate nest sites. Western Bluebirds are primarily insectivorous during breeding season, hawking flying insects from perches or dropping to ground to capture beetles, caterpillars, ants, and grasshoppers. During fall and winter, their diet shifts to include berries from elderberry, sumac, mistletoe, and other native plants. Breeding occurs from March through July, with peak activity in April and May. Females construct cup nests of grasses, pine needles, and feathers in cavities, laying 3-6 pale blue eggs. Incubation lasts 12-14 days, and nestlings fledge after 19-22 days. Pairs typically produce two broods annually in favorable conditions. The Western Bluebird is not federally or state listed and maintains stable populations across most of its range as of December 2025. However, the species experienced significant declines in the mid-20th century due to habitat loss and competition from introduced House Sparrows and European Starlings for nest sites. Conservation efforts, particularly nest box programs initiated in the 1970s, have contributed to population recovery in many areas. Current threats include continued habitat fragmentation, wildfire impacts on nesting sites, and climate change effects on insect prey availability. The species benefits from oak woodland preservation, snag retention in managed forests, and ongoing nest box maintenance programs throughout California.

Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, and more.